NEW YORK (FORTUNE) -
A couple weeks ago, my wife and I caught a lengthy but entertaining promo for the Winter Olympics on NBC. It consisted of ice skaters skating, plus a song that combined hip-hop and arena rock by a group we didn't know.

A little searching on the Web revealed that the group was Flipsyde, that Washington Post critic Geoffrey Himes considered its "largely ignored" We the People to be the best hip-hop album of 2005, and that the song played on NBC was called "Someday." A few seconds and 99 cents later it was ours.

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Which got me to thinking. The first thought was: How lame is it that I get my music-shopping ideas from Olympics ads? Which immediately led to thought No. 2: Where else am I supposed to get those ideas?

This is becoming one of the more interesting dilemmas of the new information age. The old media gatekeepers are getting weaker by the day. In the case of pop music, this is an almost unmitigated good, given how bland and craven the most powerful gatekeepers -- commercial radio stations -- had become.

It also means, as Wired editor-in-chief Chris Anderson will be telling us in great depth soon in his much-anticipated book The Long Tail: Why the Future is Selling Less of More, that more and more people will be able to make a living from songs, books, movies and other media products that appeal only to a limited audience.

Still, the new world of iTunes playlists and "customers who bought this album also bought ..." has its drawbacks as well. The main one is that it can hard to break out of whatever subculture -- of music or any other kind of media -- you've decided to join.

Sometimes this is just a case of missed opportunity: If I hadn't happened to be watching NBC that night, I wouldn't have bought that nice Flipsyde song. But it can also mean a loss of shared experience, of common reference points for a society. This has to be part of the explanation for the increasingly polarized state of political discourse in the United States: Partisans of both left and right are now able to assemble media diets that almost never contradict their preconceived views.

This is not an unprecedented state of affairs -- big American cities used to have lots of different newspapers, each with pronounced political leanings and articles explicitly shaded to reinforce those leanings. There is nothing natural or inherently superior about the monolithic media institutions of the mid-to-late 20th century.

But there is still a need for the community-building, consensus-shaping role that the best of the media gatekeepers can play. The question is, who's going to play it? And how are they going to make it work economically?

There are the existing gatekeepers, of course: Network TV, newspapers, mass-circulation magazines. Some may survive and thrive. But they'll have to do without economic advantages they enjoyed in the past. Newspapers in particular are in a panic right now. It's not so much that readers are abandoning them (they get an awful lot of traffic online) as they've lost their stranglehold on classified advertising.

For those who place classifieds or read them, the new era of Craiglist, Monster.com, and the like is undeniably better than the old newspaper-dominated one. But for decades, classified ads subsidized journalism. Now they won't.

This is the way of economic progress, and as a business journalist who has on occasion applauded creative destruction as it wreaked havoc upon other people's industries, I can't exactly complain about it.

But it does raise some subversive thoughts: Are Americans willing to pay for what's good for them? Are there great new fortunes to be made in telling us what to pay attention to, or is this business of media gatekeeping going to be chiefly a sideline (think Oprah Winfrey and her book club)? Is there a role for public broadcasting as the last uniting, subsidized medium?

And are there any more of those NBC Olympics promos coming up that I should know about?